Gold is one of metals of great value and is present as simple fine particles in natural veins. As methods which are known for recovering gold, there are methods in which gold is eluted with a cyanide solution, and in which gold is recovered as mercury amalgam.
When gold is leached with a cyanide solution, gold is dissolved as cyanide complexes. It is known that cyanide complex of gold is more stable than other types of gold complex ion. The leached gold is usually adsorbed on activated carbon, and then eluted with an aqueous solution containing mainly sodium hydroxide. Thereafter, gold is recovered from the gold-containing eluent via electrowinning.
Patent Document 1 discloses a technique to elute gold from activated carbon on which gold was adsorbed. Specifically, gold complex is adsorbed on activated carbon, and then the activated carbon is separated by filtrating through a pulp, thereafter washed by hydrochloric acid, then subjected to a heating cyanide solution to elute gold complex from the activated carbon. This technique is named CIP (Carbon in pulp), and is known as a method to obtain high purity gold.
Patent Document 2 discloses a technique to elute gold from activated carbon with alkali such as sodium hydroxide. In addition, Patent Document 3 and 4 disclose a technique to elute gold from activated carbon with aqueous solution of thiosulfate such as sodium thiosulfate.